In heavy-duty levels it is important that the frame of the level maintains stability for accurate measurement readings. It is also important that levels, which are used in professional construction on types of jobs when a level may be dropped from a substantial height and be subjected to various stresses, sustain the impact with minimal or no damage.
Many box levels have a central vial positioned into a notch which is formed by removing a section of a top wall and adjacent portions of each side wall, as seen in FIG. 1.
Because material is removed from the center of the extruded frame, a central frame section becomes the weakest portion of the extrusion. Tests have shown that in prior levels 10, the central region 11 of a frame 12 with the cut-out notch portion 20 for the central vial is substantially weak. FIG. 2 shows that in such prior levels 10 a bottom 21 of the notch 20 is the weakest region. Portions 22 of sidewalls 13 which surround the central-vial notch 20 are also substantially weak regions 22A which extend to weakened areas 22B.
It is further seen in FIG. 2 that there is also a substantial weakness in top-wall regions 23 adjacent to hand holes from which material is also removed from the level frame 12. There is a need for an improved level with a strong stable frame.